Résumés Année 2015

"A bi-stable Pt(II) based molecular turnstile"

Abstract: Playing with competition between H- and coordination-bonds, a bi-stable unsymmetrical organometallic turnstile was designed and its dynamic behaviour studied in solution by NMR techniques. The turnstile, bearing two differentiated interaction sites, is based on a stator, composed of a square planar Pt(II) centre equipped with one pyridyl group and one phenol moiety, connected to a symmetrical rotor bearing a pyridyl unit as either a H-bond acceptor or as a monodentate coordinating site. Whereas in the absence of a metallic effector, the turnstile is locked by a H-bond formed between the phenol moiety located on the stator and the pyridyl group of the rotor, in the presence of Ag+ cation, the turnstile switches to another close state resulting from the simultaneous binding of the cation by both pyridyl units belonging to the stator and to the rotor. The switching process was shown to be reversible.

Abstract: Combinations of a neutral organometallic tecton based on a square planar Pt(II) complex bearing two triphenylphosphine groups and two 4-ethynylpyridyl coordinating moieties in trans positions, with various metal halides (MX2, M = Co(II), Ni(II) Cd(II), X = Cl- or Br-) lead to the formation of 2D grid type heterobimetallic coordination networks in the crystalline phase.

Abstract: A strategy for the conversion of homometallic coordination networks into mixed metal-organic frameworks (MM’MOFs) is proposed. Ni(II) complexes of dipyrrin (dpm) ligands bearing peripheral pyridyl or imidazolyl units have been shown to self-assemble into coordination polymers with the metal cation in an octahedral environment coordinated to two bis-pyrrolic chelates and two neutral monodentate coordinating units such as pyridyl or imidazolyl moieties. Taking advantage of the chelate effect, the two monodentate units may be replaced by a diimine ligand leading to the disassembly of the networks by the formation of discrete soluble complexes. The latter can be employed as metallatectons for the construction of heterometallic architectures upon reaction with a secondary metal salt. This approach was applied using either 1,10-phenanthroline (phen) or 2,2’-bispyrimidine (bpm) as chelates leading to a series of mono- and bi-nuclear metallatectons of the (phen)Ni(dpm)2 and (bpm)[Ni(dpm)2]2 type. Subsequent assembly with CdCl2 afforded either interpenetrated 2D grid-type architectures or 3D MM’MOFs.

"Nanopatterning of surfaces with mono- and bi-metallic 1D coordination polymers: a molecular tectonics approach at the solid/liquid interface"

Abstract: The self-assembly of multiple molecular components into complex supramolecular architectures is ubiquitous in nature and constitutes one of the most powerful strategies to fabricate multifunctional nanomaterials by the bottom-up approach. When spatial confinement in two-dimensions on a solid substrate is employed, this approach can be exploited to generate periodically ordered structures from suitably designed molecular tectons. This contribution demonstrates that physisorbed directional periodic arrays of monometallic or heterobimetallic type may be generated on HOPG surface by combinations of properly design directional organic or metallatecton based on a porphyrin or Ni(II) metallaporphyrin backbone bearing a pyridyl and a terpyridyl coordinating sites with CoCl2. The periodic architectures were visualized at the solid-liquid interface with a sub-molecular resolution by Scanning Tunneling Microscopy corroborated by DFT calculations.

"From hydrogen bonding to metal coordination and back: A porphyrin based networks on Ag(111)"

Abstract: The self-assembly of a metal-free porphyrin bearing two pyridyl coordinating sites and two pentyl chains at trans meso positions was investigated under ultrahigh vacuum on a Ag(111) surface by scanning tunneling microscopy (STM). The STM measurements revealed a well-ordered close-packed structure with a rhombic unit cell for coverages ≤ 1 monolayer with their molecular plane parallel to the surface. The growth direction of the molecular islands is aligned along the step edges, which are restructured due to molecule-substrate interactions. The shorter unit cell vector of the molecular superstructure follows the ⟨1-10⟩ direction of the Ag(111) substrate. Hydrogen bonds between pyridyl and pyrrole groups of neighboring molecules as well as weak van der Waals forces between the pentyl chains stabilize the superstructure. Deposition of cobalt atoms onto the close-packed structure leads to the formation of a hexagonal porous network stabilized by metal-ligand bonding between the pyridyl ligands and the cobalt atoms. Thermal annealing of the Co-coordination network at temperatures > 450 K results in the transformation of the hexagonal network into a second close-packed structure. Changes in the molecule-substrate interactions due to metalation of the porphyrin core with Co as well as intermolecular interactions can explain the observed structural transformations.

"On Zn(II) 2,2’-bisdipyrrin circular helicates"

Abstract: Coordination of two 2,2’-bisdipyrrin ligands, bearing methyl ester or methylthioether peripheral groups, with Zn(II) cations leads not only to the formation of the expected linear helicates but also concomitantly to novel tri- and tetra-nuclear circular species that have been isolated and fully characterized in solution and by single-crystal X-Ray diffraction.

Abstract: A chiral-at-metal Ir(III) organometallic metallatecton was synthesised as a racemic mixture and as enantiopure complexes and combined with Cu(II) to afford a heterobimetallic (Ir,Cu) grid- type 2D coordination network.

Abstract: Bridging the gap between microscopic (atoms and molecules) world and macroscopic molecular architectures is a challenging task requiring the development of construction strategies. Molecular self-assembly is a possible answer provided that one can program the construction processes at the molecular level. Among different forms of solids, the world of crystals is particularly fascinating. These macroscopic solid-state materials composed of atoms and molecules are periodic and ordered. Molecular tectonics, an approach at the crossroad between supramolecular chemistry and solid state molecular chemistry, deals with this type of organisation through molecular programming of individual atoms and molecules. For this approach, crystals are seen as molecular networks composed of construction units called tectons interconnected through supramolecular reversible intermolecular interactions based on molecular recognition events. Through some selected examples dealing with emerging properties resulting from molecular organisation, the scope of molecular tectonics is discussed.

Abstract: Two tetrasubsituted derivatives of tetramercaptothiacalix[4]arene in 1,3-alternate conformation bearing either four (3-cyano)propyl or (4-cyano)benzyl moieties have been synthesized and characterized in solution as well as in the solid state by X-ray diffraction on single crystals. Their propensity to form coordination networks was investigated in the presence of silver cation as connecting metal and hexafluorophosphate as counter ion. Whereas the combination of AgPF6 and 1 bearing four (3-cyano)propyl groups leads to a 1D silver coordination network, for 2, containing four (4-cyano)benzyl units, a 3D diamond-like architecture is obtained.

"Molecular tectonics: grid and porous coordination networks based on combinations of iron thiocyanate and tetrathiacalix[4]arene and tetrathiatetramercaptothiacalix[4]arene pyridyl appended derivatives"

Abstract: The combinations of three pyridyl appended tetrathiacalix[4]arene (TCA) and tetramercaptotetrathiacalix[4]arene (TMTCA) derivatives in 1,3-A imposed conformation behaving as neutral tectons with octahedral FeII(NCS)2 complex as a metallatecton leads to the formation of new coordination networks. Whereas the tecton 4, a tetrasubstituted TCA derivative (pyridyl in ortho position) leads to a 2D grid-like network, for the other two tectons 5 and 6, the formation of 3D diamond-like architectures are observed.

Abstract: With the aim of combining luminescence and chirality in heterometallic Ir(III)-Cd(II) coordination networks, synthetic strategies for the formation of new Ir(III)-based chiral metallatectons ([Ir(dFppy)2(1)][PF6]), both as a racemic mixture of D and L enantiomers (rac-[Ir(dFppy)2(1)][PF6]) and as enantiopure complexes (D-[Ir(dFppy)2(1)][PF6] and L-[Ir(dFppy)2(1)][PF6]), were developed. The final compounds were characterized both in solution and in the crystalline phase. Notably, their crystal structures were determined by single crystal X-ray diffraction and their photophysical properties in solution and in the solid state were investigated. Combination of the cationic linear metallatecton with Cd2+ iodide salt ([CdI3]-), behaving as an anionic two-connecting node, leads to the formation of 1D chiral and neutral heterometallic Ir(III)-Cd(II) luminescent coordination networks both as a racemic mixture and as enantiomerically pure infinite architectures. The latter have been structurally studied in the solid state by X-ray diffraction both on single crystals and on microcrystalline powders. The infinite coordination networks display phosphorescence in the solid-state at ca. 600 nm upon excitation at 400 nm.

"Welding Molecular Crystals"

Abstract: Both for fundamental and applied sciences, the design of complex molecular systems in the crystalline phase with strict control of order and periodicity at both microscopic and macroscopic levels is of prime importance for developments of new solid state materials and devices. The design and fabrication of complex crystalline systems as networks of crystals displaying task specific properties is a step towards smart materials. Here we report on isostructural and almost isometric molecular crystals of different colours, their use for fabrication of core-shell crystals and their welding, by 3D epitaxial growth, into networks of crystals as single crystalline entities. Welding of crystals by self-assembly processes into macroscopic networks of crystals is a powerful strategy for the design of hierarchically organised periodic complex architectures composed of different subdomains displaying targeted characteristics. Crystal welding, may be regarded as a first step towards the design of new hierarchically organized complex crystalline systems.